In order to pursue our overall objective of finding specific means of altering the expression of the transformed genome of mammary epithelial cells, whether they be preneoplastic or neoplastic, we have a) studied the influence of dietary lipids on the growth rate of transplantable mammary adenocarcinomas in both virus-infected and uninfected mouse strains and b) performed membrane studies with isolated cells from both normal and tumor murine mammary tissues. Our dietary studies have revealed that whereas those diets which contain polyunsaturated fatty acids are most effective in stimulating tumor growth, it is the availability of arachidonate rather than its conversion to prostaglandins which is involved in this enhancement. Our studies of the surface of mammary epithelial cells during their transition from a normal to a neoplastic phenotype are directed towards developing methods to monitor such changes. We have investigated the activities of 5'-nucleotidase and galactosyl transferase on cell surface membranes and have found them to be promising markers of such processes when used with isolated cells growing in monolayer cultures. In addition, we have developed immunofluorescence techniques for the identification of mammary cells in culture. These methods are aimed at identifying specific cell surface antigens and can now be used to distinguish between epithelial cells, fibrocytes, and adipose cells with a good degree of certainty.